#include <stdio.h>
int main()
{
	int a = 0, b = 0, c = 0;
	scanf("%d %d %d", &a, &b, &c);
	float sum = 0;
	for ( int i = 1; i <= a; i++ ) {
		sum += i;
	}
	
	for ( int i = 1; i <= b; i++ ) {
		sum += i * i;
	}	
	
	for ( int i = 1; i <= c; i++ ) {
		sum += 1.0/i;
	}
	printf("%.2f", sum);
	return 0;
}
